Wrought nickel base alloy article

ABSTRACT

A WROUGHT, DUCTILE NICKEL BASE SUPERALLOY ARTICLE ALLOWS INCLUSION OF RELATIVELY LARGE AMOUNTS EACH OF THE GAMMA PRIME STRENGTHENERS AL, TI AND CB, FOR EXAMPLE IN COMBINATION BY WEIGHT, 3-4% AL, 2-3.5% TI AND 3-5% CB, WHILE MAINTAINING IMPROVED TENSILE DUCTILITY AND CREEP RUPTURE STRENGTH THROUGH A PROCESSING PROCEDURE EMPLOYING RELATIVELY LOW TEMPERATURE SOLUTIONING, AND PREFERABLY A PRELIMINARY AGING PRIOR TO SOLUTIONING.

April 27, 1971 J, F, BARKER ET AL t 3,576,681

v WROUGHT NICKEL BASE ALLOY ARTICLE Filed March 2, 1969 2 Sheets-Sheet 1 STANLEY F. STIRNSTY CARI. 5. WUKUICK agua April'zz 1971 Filed March 26, 1969 J. F. BARKER Er AL 3,576,681

wnu' NCKEL BASE ALLOY ARTIGLE 2 sheets-sheet a JAMES F'. BARKER EUGENE L. DUNN STANLEY F. STERNASTY CARL S. WUKUSICK Arnau IV United States Patent O I WROUGHT NICKEL BASE ALLOY ARTICLE James F. Barker, Eugene L. Dunn, Stanley F. Stemasty,

and Carl S. Wukusick, Cincinnati, Ohio, assignors to General Electric Company Filed Mar. 26, 1969, Ser. No. 810,611 Int. Cl. C22c 19/00 U.S. Cl. 148-32 5 Claims ABSTRACT F THE DISCLOSURE A wrought, ductile nickel base superalloy article allows inclusion of relatively large amounts each of the gamma prime strengtheners Al, Ti and Cb, for example in combination by weight, 3-4% Al, 2-3.5% Ti and 3-5% Cb, while maintaining improved tensile ductility and creep rupture strength through a processing procedure employing relatively low temperature solutioning, and preferably a preliminary aging prior to solutioning.

A signicant factor in the evolution of advanced power producing apparatus, such as a gas turbine engine, is the successful development of improved materials. `One type of material of significant interest has been the nickeldbase superalloy applied both as a casting alloy as well as produced as a wrought alloy article in the form of ingot, slab, bar, rod, sheet, forgings, etc. as well as in the form of engine components. l

In the higher temperature operating sections of such power producing apparatus as jet engines for aircraft use, increase in temperature capability of alloys with the sarne and preferably better mechanical properties is the subject of continuing study. However, in those engine sections operating at intermediate temperatures, for example, in the range of about 900-l400 F. higher strength-todweight ratios as well as alloy stability and ductility are extremely important.

A principal object of the present invention is the provi-y Varticleof-aimproved--ductility andcreep rupture strength in the intermediate temperature range of about 900-l400 Another object is the provision of such an improved nickel-base superalloy as a forged article having high strength properties andductility in the intermediate tem-Y perature range of about 900`1200 F.

These and other objects and advantages will be more fully recognized and appreciated from the following more detailed description including the drawing and representative examples which are typical of the present invention.

-In the drawings:

FIG. l is a graphical comparison of stress rupt-ure strength of the present invention with known alloys;

FIG. 2 is a graphical .comparison of 0.2% yield strength data of the present invention with known alloys;

FIG. 3 is a graphical presentation of creep data; and

FIG. 4 is a graphical presentation of tensile data and a comparison with known alloys.

vStrengthening mechanisms in modern high strength nickel-base superalloys generally include the precipitation strengthening and the solution strengthening types. Although the precipitation of carbides is influential on the properties of such alloys, a more effective strengthening Patented Apr. 27, 1971 l Ce precipitate is gamma prime, Nia (Al, Ti), sometimes modied to include Cb. Control of such a mechanism has allowed development of relatively high tensile and stress rupture properties at elevated temperatures. However, the levels and relationships between such elements as Al, Ti and, when used, Cb are critical because the properties obtainable from the gamma prime strengthening precipitate can vary between wide extremes depending upon the kind of structure and phases formed.

Combined with the precipitate strengthening mechanism in a nickel-base superalloy is the solution strengthening mechanism resulting from the inclusion of a variety of vsolid solution forming elements. The most commonly used elements for such purpose have been Cr, Co, Mo and W, although Cr and Co generally are added more for oxidation resistance and hot workability, respectively, than for strengthening effects. Thus, Mo and W have been used as the major solution strengtheners.

One aspect of the present invention recognizes a particular critical relationship between the elements Al, Ti and Cb which allows their use together at higher concentrations. The major strengthening mechanism in the present invention results from the combination of such elements with nickel to allow the formation of a tine generally discrete gamma prime or Nia (Al, Ti, Cb) dispersion. In the absence of Cb in gamma prime strengthened nickel-base superalloys, the optimum Al/Ti ratio appears to be about 1. However, as Cb is added, the strength is sharply increased. It has been recognized that the gamma prime stability can be enhanced while increasing the strength of the alloy by including Cb in the range of about 3-5 weight percent with 3-4% A1 and 2-3.5% Ti. As the gamma prime phase is enriched with Cb, the relative Al concentration must be increased to stabilize the cubic structure of Nia (Al, Ti, Cb) over the Nia `Cb or Nia Ti phases which are not effective strengtheners.

Cb is included in the alloy of the present invention in the range of about 3-5 weight percent. Ordinarily, a total content of Al, Ti and Cb in the range of about 8-12 weight percent would result in an alloy of low ductility.

. .Howeven it has been found that with the particular combination of elements defined by the present invention, good ductility and creep strength can be maintained through novel processing more particularly described later and in concurrently led co-pending application Ser. No.

810,612. Thus, the combination of elements in the present invention allows definition of a different strengthening arrangement than has heretofore been recognized, allowing the inclusion of larger amounts of `Cb in the range of about 3-5 Weight percent along with 3-4% A1 and 2-3.5% Ti.

Because the present invention is particularly directed to a wrought alloy article, control of carbides formed in the alloy range of the present invention is important. The carbide forming elements included in the present invention are Ti, Cb, Cr, Mo and W. Ti and Cb usually form a simple MC type carbide whereas the other carbide formers provide complex carbides of the MaaCa and MSC type carbides. The complex carbides are formed at lower temperatures than are the simpler carbides and are less stable. It is believed that the complex carbides form as a result of breakdown of the simpler MC type carbides during hot working operations or during aging, or both, because of the presence oficarbon in excess of that accommodated by the MC carbide forming elements. Therefore, fwhile it is important that carbon be included in the alloy of the present invention for the precipitation of stable carbides, it is also important that excessive carbon be excluded. The present invention recognizes that with the particular combination of elements which define the unusual gamma prime and solution strengthening mechanisms, carbon should be included in the range of about 0.050.25 and preferably 0. 1-O.2%

Coupled with these and other criticalities in composition of the alloy of the present invention, as described in more detail later, is a processing procedure involving the utilization of a relatively low solutioning preferably coupled with a preliminary aging prior to solution to improve tensile ductility and creep strength. 'I'he preferred form of such processing involves aging at about 1550- l750 F. and preferably l600-l700 F. before solutioning at about 190042100 F.

The alloy composition of the present invention, which has been found to provide the improved combination of properties consists essentially of, by weight, 34% Al, 2-3.5% Ti, 3-5% Cb, Mo and W in an amount such that the sum of the Mo and half of the W is in the range of 4-8%, 516% Co, 9-16% Cr, 0.05-0.25% C, 0.005- 0.03% B, up to about 0.1% Zr with the balance Ni and incidental impurities. The preferred form of such an alloy consists essentially of, by weight, 3-4% Al, 2-3% Ti, 3-5% Cb, 3-5% Mo, 3-5% W, 5-16% Co, 13-16% Cr, 0.1-0.2% C, Q01-0.02% B, 0.01-0.1% Zr, with the balance nickel and incidental impurities. As will be shown in some detail later, Fe in amounts more than as an impurity is detrimentalto certain mechanical properties of the alloy article and is not a substitute for any portion of lthe elements Ni and Co with which it chemically is closely related.

Typical of a wide variety of alloys melted and tested in the evaluation of the present invention are those shown in the following Table I.

TABLE I [Weight percent-balance Ni and incidental impurities] Example Al Ti Cb Mo W Co Cr C B Zr TABLE II [Tensile strength data (p.s.i. X10-3)] Ultimate strength, temper- 0.2% yield strength, temperatures F.)

atures F.

Example Room 1,000 1,400 Room 1,000 1,400

Although commercially available alloys represented by the composition of Examples `6 and 7 presently are used in components for jet engines, the alloy of the present invention has significantly improved properties. For example, the graphical comparison of FIG. 1 shows the average stress rupture strength of the alloy forms within the scope of the present invention, as represented by the Table I compositions, is signicantly improved over the known alloys.

In FIG. 1, the abscissa identities the Larson-Miller parameter P Widely used in the metallurgical art and described in more detail in American Society of Engineers Transactions 1952, volume 74, at pages 765-771.

As was mentioned before, the alloys of Table I were solutioned at the relatively low temperature of about 195 0 F. Normally, higher solution temperatures are used for alloys of this type. However, it has been recognized that solutioning of an alloy article, which in the interpretation of the present invention is intended to include an ingot or slab, at a relatively low solutioning temperature in the range of about l900-2100 F., develops improved tensile properties in the article even though the alloy includes an unusually high combination of gamma prime strengtheners in the range of, by weight, 34% A1, 23.5% Ti, and 3-5% Cb.

Another series of alloys melted and tested in the evaluation of the present invention are represented by those shown in Table III.

TABLE III [Weight pereent-balance Ni and incidental impurities] CrC The alloys identified by the composition of Examples 1, 2 and 3 are within the scope of the present invention whereas those of Examples 4, 5, 6 and 7 are outside its scope, with Examples 6 and 7 representing two commercially available alloys used in jet engine components. The alloys of Table I were all prepared by vacuum melting prior to casting into ingots or slabs for further processing.

One series of alloy forms represented by Examples 1 through 5 of Table I were vacuum melted and cast into slabs prior to being processed into sheet. The slabs were homogenized at 2150 F. before solutioning `at about 1950 F. followed by air cooling. The material was then hot rolled to about 0.08" thick sheet and then cold rolled to about 0.06-0.07 thick sheet. 'Ihus such highly strengthened alloys as a result of processing were sufciently duc- The alloys of Table III were consolidated by vacuum melting of high purity metals. Examples 13 and 14 represent two other well known and widely used commercially available wrought alloys, presented for comparative purposes. The other alloys represented by the compositions shown in Table III were melted into pound heats, the ingots from which were primarily broken down into forms by extrusion. Secondary working was accomplished by further extrusion to bar stock, hammer or press forging or broad or flat rolling. A variety of tensile tests were conducted primarily at room temperature, 1000 F., 1200 F. and 1400 F. while creep and stressrupture tests were conducted primarily at 1000 F. and

FIG. 2 is .a graphical comparison of the 0.2% yield strength of rthe alloy form of Example '8, within the TABLE IV.-CREEP RUPTURE [1,200 F.-170,000 p.s.i.]

Elon- Reduction Rupture gatlon, in arca,

Example life, hours. percent percent In addition to -the advantage of the alloy of Example S over the forms of Examples 1l and 12 as shown in Table IV, tests at l200 F. and 150,000 p.s.i. disclosed the alloy form of Example 8 to have a creep rupture life of 512 hours compared with a life of only 8 hours for the alloy of Example 12.

As has been shown above, the present invention recognizes that a wrought nickel-base superalloy including an unusually high and particular combination of the garnma prime strengtheners Al, Ti and Cb can be provided with certain improved properties through a processing procedure employing a relatively low temperature solutioning. In addition, it has been recognized that still better properties for certain uses can be developed in the present invention through a type of processing described in greater detail in co-pending and concurrently led application Ser. No. 810,612.

In general, the improved processing described in that co-pending application involves the use of a preliminary aging procedure prior to solutioning. As it relates to the present invention, it is recognized that the improved properties can be attained as a result of preliminary aging in the temperature range of about 1550-1750" F. for example, although alloy form 8, within the scope of the present invention, has been shown to have good tensile ductility and to have significantly greater strength properties than known alloy forms, its properties can be further enhanced by particular processing.

The alloy of Example 8 was provided as 1A to 1% diameter bar stock prepared by rod-rolling previously extruded stock. The bar stock was homogenized at 2000 F. and air cooled prior to final processing to insure relative uniformity in structure.

Ordinarily, final processing of nickel base superalloys of the type to which the present invention relates involves first solutioning at a relatively high temperature prior to subsequent aging. However, in accordance with the invention of the above identified co-pending application, one group of specimens from the alloy of Example 8 were -frst preliminarily aged for about a day at a series of temperatures ranging from about l450-l850 F. The speci- -mens were then subjected to the relatively low solutioning temperature in the range of l9002l00 F. prior to final aging.

An example of the unusually great improvement in creep properties which can be attained through this type of processing is that represented by the creep data shown in FIG. 3. In that particular example, after the preliminary aging for about 24 hours at the temperatures shown, the bar stock was solutioned at 2000 F. Finally each specimen in that series was double aged, first at 1100 F. and then at 1350 F.

In another example, a flat 1" thick forging of the alloy of Example 8 was prepared. It was preliminarily aged at about 1650 F. prior to solutioning at about 2000 F. and then aged as described above in connection with the data of FIG. 3. Typical of the significantly improved tensile properties obtained from such a forging are the data presented in graphical form in FIG. 4. In addition, FIG. 4 compares the 0.2% yield strength of the present invention with that of the two known wrought nickel base superalloys as represented by the compositions of Examples 13 and 14 in Table III.

Additional flat forgings of the' type described in connection with the alloy of Example 8 were prepared from the alloys of Examples 9 and 10 within the scope of the present invention. After homogenization and finish forging, test specimens were prepared and heat treated in the preferred method as described in connection with the data of Examples 3 and 4. Table V shows the excellent l000 F. tensile data for the alloys of Examples 9 and 10 representing the lower chromium range of the present invention. Noteworthy, in addition to the high strength properties is the excellent ductility developed as a result of the particular combination of elements combined with the improved processing as defined by one form of the present invention.

TABLE V [1,000" F. tensile data] Strength p.s.i. X10-3 Percent Thus, it is easily seen, for example from the data of FIGS. 3 and 4, that the present invention provides an alloy article form of significantly improved tensile and creep properties resulting from a particular combination of elements processed at a relatively low solution temperature and preferably processed to include a preliminary aging step prior to such solutioning.

As was mentioned before, it is important that carbon be included in the alloy of the present invention in the proper range for the precipitation of stable carbides. The presence of the proper type and the amount of canbides is significant in grain size control in subsequent processing. Addition of carbon up to about 0.05% functions as a deoxidizer.

Like carbon, zirconium is added in part for deoxidizing purposes. However, retention of amounts up to about 0.1% assists in the provision of higher creep rupture ductility.

Cobalt is included in the alloy of the present invention for ythe `double purpose of improving workability and as a solution strengthener. However, it is recognized that it also may stabilize the gamma prime.

In the alloy of the present invention, Cr is required in the matrix to allow the formation of the super-saturated solution with the amounts of Al, Ti and Cb hardeners in the alloy. Thus it affects the solubility of the gamma prime hardeners. Cr is required in amounts of at least about 9 weight percent to assist in the precipitation of substantial amounts of gamma prime.

As has been shown from the data, the inclusion of Fe does not improve strength properties and is, in fact, detrimental to certain strength properties at temperatures above about l000 F. Too much Fe results in the formation of excessive mu and other detrimental intermetallic phases. In addition, it results in low temperature brittleness and low strength at high temperatures.

What is claimed is:

1. A wrought nickel =base alloy article of improved tensile ductility and creep properties as a result of solutioning in the range of 1900-2l00 F., the alloy of the article consisting essentially of, by weight: 3-4% Al, 2- 3.5% Ti, 3-5% Cb, Mo and W in an amount such that the total of Mo and half of the W is in the range of 4- 8%, 5-16% Co, 9-l6% Cr, 0.050.25% C, 0.0050.03% B, up to about 0.1% Zr with the balance nickel and incidental impurities.

3. The article of claim 1 in which the alloy consists f essentially of, by weight: 3-4% Al, 2-3% Ti, 3-5% Cb, 3-5% Mo, 3*5% W, 5-l6% Co, 13-16% Cr, C21-0,2% C, 0.01-0.02% B, 0.0l-0.1% Zr, with the balance nickel and incidental impurities.

4. The article of claim 3 in which the alloy consists essentially of, by weight: 3.3-3.7% A1, 22a-2.7% Ti, 3.3-3.7% Cb, 3.3-3.7% Mo, 3.3-3.7% W, 7-9% Co, 13-15% Cr, 0.13-0.17% C, (lOl-0.02% B, 0.03-0.7% Zr with the balance nickel and incidental impurities.

5. The article of claim 1 in the form of a forged disc which 'has been prelirninarily aged at about 1600-1700 LF.

prior to solutioning at a temperature in the range of about 1950-20\50 F.

References Cited UNITED STATES PATENTS 2,912,323 1l/l959 Bieber et al. 75-171 3,046,108 7/1962 Eiselstein 75-171 3,403,059 9/1968 Barker 14S-32.5

10 RICHARD O. DEAN, Primary Examiner U.S\. Cl. X.R.

ggsgg@ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 576J 681 Dated ABrl 27, 1971 Inventor(s) J. F. Barker et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 2, after "about" delete 155 and insert --1550 in plac thereof.

Column 7, line 12, after "0. 03" delete 0. 7 and insert O. 07 in pla thereof.

Signed and sealed this Zllth day of August 1971.

(SEAL) Attest:

EUJARD M.FLETCHER,JR. WILLIAM E. SCHUYIER, JR. Attesting Officer Gomissioner of Patents 

